The only rules are these:
1. Be respectful to other role-players and their characters.
2. Try not to add different storylines at one time to the role-play. Trust me, I've seen this happen before and it makes the role-play very confusing and hard to keep track of.
3. If your character's actions are meant to invoke a response from another role-player's character, try to keep it vague. It's not necessarily fair to another role-player if you're dictacting their next move in your post.
Example:
Natasha struck out at Cornelius, stabbing him in the heart and causing him to fall to floor, writhing in pain and begging for mercy. (Cornelius could've had several opportunities to respond to any one of Natasha's actions, but never had a chance to. This instills a negative feeling for the role-player who plays Cornelius and may not want to return to the topic, which could be bad if Cornelius was an important character in the role-play.)
Example:
Natasha struck out with her blade, aiming for Cornelius's heart. (This is quite vague and allows Cornelius to respond to either block or get hit and react from there. This allows the topic to be more open to other role-players also.)
Well, there ya have it! Let's keep it clean and fair folks! Enjoy!